Discovery of blood vessel system in bones

Network supplies bones and helps immune cells to quickly reach the sources of inflammation.

Although bones are very hard organs, they also have a dense network of blood vessels inside them where the bone marrow is located as well as on the outside that is covered by the periosteum. This is why bone fractures often cause serious bleeding.

A young scientist- Dr. Anika Grüneboom at Universitätsklinikum Erlangen has recently discovered a network of very fine blood vessels that connect bone marrow directly with the blood supply of the periosteum that was previously overlooked.

Dr. Grüneboom, Department of Medicine 3 – Rheumatology and Immunology at Universitätsklinikum Erlangen said, “As with every organ, bones need a closed bloodstream for these functions. While fresh blood is transported into organs via arteries, veins transport the ‘used’ blood back out again. The precise structure of this closed bloodstream in long bones was not clear up to now.”

Dr. Grüneboom made this discovery while working on her doctoral thesis at Universität Duisburg-Essen (UDE) with Prof. Dr. Matthias Gunzer.

A chemical process that makes bones transparent enables scientists to view the structures inside them. Young researcher Dr. Anika Grüneboom discovered the so-called trans-cortical vessels (white arrows) – they connect the blood supply of the bone marrow with the periosteum. (Image: UDE/Matthias Gunzer, Anika Grüneboom)
A chemical process that makes bones transparent enables scientists to view the structures inside them. Young researcher Dr. Anika Grüneboom discovered the so-called trans-cortical vessels (white arrows) – they connect the blood supply of the bone marrow with the periosteum. (Image: UDE/Matthias Gunzer, Anika Grüneboom)

Along with her colleagues, Dr. Gruneboom now discovered thousands of previously unknown blood vessels in the bones of mice that traverse perpendicularly across the entire length of the compact bone, the so-called cortical bone.

The specialists have named them ‘trans-cortical vessels’ (TCVs) consequently. Besides, they could exhibit that most of both blood vessel and venous blood flows through this newfound system of vessels. This implies the framework is a central component for providing bones with oxygen and nutrients.

When examining them, scientists found that these blood vessels is used by the immune cells in bone marrow to reach the bloodstream. In the case of inflammatory diseases such as arthritis, it is especially important that immune cells reach the source of the inflammation quickly.

Dr. Grüneboom said, “This network of blood vessels in the bone is similar to an underground train system that is able to successfully transport large numbers of passengers quickly and directly through barriers.”

Lead researcher Prof. Gunzer adds: “The previous concepts only described a few single arterial canals and two venous canals in bones. This is completely inaccurate and does not reflect the actual situation at all. It is quite surprising that we can still find new anatomic structures in the 21st century that are not found in any textbooks.”

“The discovery was possible due to a unique combination of modern imaging methods. Many of these methods were used for the very first time by us such as so-called light-sheet fluorescence microscopy and ultra high-resolution 7 tesla (T) magnetic resonance imaging and x-ray microscopy in collaboration with the ERC Synergy Grant 4D-nanoSCOPE team under the leadership of Prof. Dr. Silke Christiansen and Prof. Dr. Georg Schett.”

Scientists are further planning to investigate the role of trans-cortical vessels for normal bone remodeling and in conditions such as osteoporosis or tumors that metastasize in bones. The work at FAU was funded by collaborative research center 1181 as well as the ERC Synergy Grant 4D nanoSCOPE.

The study is published in the journal Nature Metabolism.

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